1. Field of the Invention
The present invention relates to a method of obtaining a ceramic laminated compact by compression-compacting a ceramic laminate which is formed by stacking a plurality of ceramic green sheets.
The present invention is directed to a ceramic laminated compact which is to be obtained during a process for manufacturing an electric or electronic component such as a capacitor, an inductor, a multilayer substrate or the like, for example. In order to obtain a large number of such components, the ceramic laminated compact is cut into independent components, which are then subjected to a firing step. Alternatively, the ceramic laminated compact is directly subjected to a firing step in order to obtain a single component.
2. Description of the Background Art
Hydrostatic pressing, which can uniformly apply pressure for compression compacting, is watched as effective means for obtaining the aforementioned type of ceramic laminated compact.
For example, Japanese Patent Laying-Open Nos. 9718/1986 and 159719/1986 disclose methods of obtaining ceramic laminated compacts through hydrostatic pressing. According to the former literature, a ceramic laminate is held between two flexible sheets, whose peripheral edge portions are sealed to vacuum-package the ceramic laminate. Then, the vacuum-packaged ceramic laminate is subjected to hydrostatic pressing. According to the latter literature, on the other hand, a frame is provided around a ceramic laminate, which is held between two flexible sheets. A space defined by the two flexible sheets and the frame is evacuated, and then the ceramic laminate covered with the flexible sheets is subjected to hydrostatic pressing.
In each case, however, both surfaces of the ceramic laminate are merely covered with the flexible sheets, and hence a flat state of the ceramic laminate is easily damaged by partial bending or the like.
In order to solve such a problem, there has been proposed a method of arranging a rigid body along one major surface of a ceramic laminate. This method is basically disclosed in Japanese Patent Laying-Open No. 292309/1986.
FIG. 11 shows this method. As shown in FIG. 11, a ceramic laminate 3 obtained by stacking a plurality of ceramic green sheets is introduced into a cavity 1 which is provided in a die 2. Then, as shown in FIG. 12, the ceramic laminate 3 and the die 2 are introduced into a bag 4, which is made of a flexible sheet material, to be protected against water. Thereafter the bag 4 is evacuated and its opening is sealed by thermal welding, for example, at a portion 5. The bag 4 containing the ceramic laminate 3 and the die 2 is submerged in water, and then pressure is applied to the water. Thus, the ceramic laminate 3 is subjected to compression compacting on the basis of hydrostatic pressure, thereby to obtain a ceramic laminated compact.
However, the hydrostatic pressing in the aforementioned mode has the following problem:
Noting modes of force acting on major surfaces of the ceramic laminate 3, one major surface (lower surface) of the ceramic laminate 3 is in contact with the bottom surface of the cavity 1 provided in the die 2, which serves as a rigid body, while hydraulic pressure is directly applied to the other major surface (upper surface) through the bag 4. This results in the configuration of a ceramic laminated compact 6 shown in FIG. 13, for example.
Referring to FIG. 13, the ceramic laminated compact 6 to be worked into electrical or electronic components is provided therein with internal electrodes 7, which are formed by printing or the like. Thus, projections 8 are formed on the upper surface of the compact 6 in portions provided with the internal electrodes 7, although the compact 6 has a flat lower surface. Such projections 8 extremely protrude as the number of stacking of the internal electrodes 7 is increased.
When the aforementioned compact 6, which is provided with the projections 8 on only one surface, is adapted to manufacture chip components, for example, appearances of such chip components are vertically asymmetrized due to projections, corresponding to the projections 8, which are provided only in first surfaces. Such vertically asymmetrical chip components are unpreferable in appearance, while imperfect contact may be caused between the electrodes of the chip components and conductive parts provided on substrates when the chip components are mounted on the substrates.